The invention described herein relates to dynamo-electric machines and more particularly to a homopolar generator-motor useful in reversibly storing and transferring energy in a thermo-nuclear reactor power generation system.
Homopolar machines conventionally are designed to produce high current, low voltage power to loads demanding very large direct currents, such as that required in metallurgical or research applications. Because the machine armature moves in a field of unchanging polarity, it generates DC power without the need for commutation, and it is this characteristic which makes the generator particularly attractive in supplying very large pulses of direct current to connected loads.
One such load represented by a fusion reactor, operates on the principle of plasma heating and confinement which requires high energy storage and transfer systems. These systems act to rapidly pulse the reactor magnetic field or load coils which compress and confine the plasma as the energy is transferred between the electrical power source and reactor load coils. Should the power source comprise a homopolar machine, the machine must operate at unusually high power densities, and the energy pulses must be transferred under very low loss conditions and in extremely short time periods, e.g., in tens of milliseconds. This energy transfer time represents the ratio of stored energy in the machine to the average power level during the pulse. In conventional homopolar machines, the ratio or transfer time, is two orders of magnitude greater than the short time requirements established for efficiently pulsing the magnetic load coils of fusion reactors.
Consideration has been given to the use of conventional homopolar machines to pulse the reactor load coils to achieve the desired reactor performance. In such an arrangement, the homopolar machine is connected to the fusion reactor load coils through a series switch and when the machine current reaches the desired value and is transferred to the coil, a shunt switch across the coil is closed to short it through a low resistance path and thus confine the current to the coil. However, at this particular instant in the cycle, voltage will still appear on the rotor winding because the mass represented by the machine rotor will cause the rotor to continue rotating. It is apparent that as rotor rotation continues with the field winding energized, the rotor conductors cut flux and continue to generate a voltage until the rotor stops.
Therefore, at the instant the shunt switch is closed, it also is necessary to open the series switch and disconnect the homopolar machine from the load to prevent its rotor from being shorted by the shunt switch. Since a high dc current at high voltage is still on the machine, it is evident that an extremely large interrupting series switch would be required to open the circuit. If such a switch could be designed, the loss of energy associated with the interruption would nevertheless be so great that it would not be compatible with the efficiency requirements for the system. For these reasons conventional homopolar machines cannot effectively satisfy fusion reactor load coil requirements because the machine design and characteristics preclude matching the energy stored in the machine with the energy to be transferred to the reactor load coils.